A typical axial flow, industrial gas turbine engine has a compression section, a combustion section, and a turbine section. An annular flowpath for working medium gases extends axially through the sections of the engine.
At the inlet to the compression section, the gases are primarily air. As the working medium gases are flowed along the flowpath, the gases are compressed in the compression section causing the temperature and the pressure of the gases to rise. The temperature of the gases exiting the compression section may exceed eight hundred (800) degrees Fahrenheit.
The hot, pressurized gases are flowed from the compression section to the combustion section. In the combustion section, the gases are mixed with fuel and are burned to add energy to the gases. These heated, high energy gases are expanded through the turbine section to produce useful work, such as by driving a turbine rotor that powers the compressor and by driving a second (or free) turbine which may be drivingly connected to a pump or electrical generator.
The combustion section includes one or more combustion chambers and a plurality of fuel injectors for supplying air and fuel to the combustion chambers. Examples of such fuel injectors are shown in U.S. Pat. No. 4,327,547 issued to Hughes et. al. entitled "Fuel Injectors" and U.S. Pat. No. 4,337,618 issued to Hughes et. al. entitled "Gas Turbine Engine Fuel Burners". The fuel injectors shown in these patents are capable of burning liquid fuel and gaseous fuel. Each fuel injector incorporates a water injection system for supplying water to the burning fuel to reduce the formation of nitrogen oxides (NO.sub.x).
The fuel injector shown in U.S. Pat. No. 4,337,618 has an inner wall extending circumferentially about an axis to bound an inner chamber for receiving air from an upstream location, such as the discharge of the compressor. A pintle disposed in the inner chamber extends axially through the chamber and downstream of the chamber to define an annular passage 62 for the air.
As the air is flowed along the passage in the inner air chamber, fuel is discharged into the air so that mixing of the fuel and air takes place within the inner chamber, thus premixing the fuel and air within the fuel injector. An annular second passage 68 outwardly of the first passage 62 provides a flowpath for air and water. A gaseous fuel is flowed through a third passage 44,46 which is disposed radially outwardly of the first two passages.
The fuel, air and water are discharged into the combustion region of the combustion chamber where the gases are ignited and burned. As the gases are burned downstream of the injector nozzle, the hot gases may recirculate through a location adjacent to the pintle and may, in some constructions, cause overheating of the pintle with an adverse effect on the durability of the pintle. In addition, the recirculating gases may ignite the liquid fuel and air mixture within the inner chamber causing further heating of the end of the pintle. If the pintle is hollow as shown in U.S. Pat. No. 4,327,547, the recirculating gases may extend axially upstream into the pintle, causing further heating of the pintle on the interior of the pintle.
Scientists and engineers under the direction of Applicants' Assignee are working to improve fuel injector assemblies and particularly: (1) to improve the mixing of liquid fuel and air and the mixing of gaseous fuel and air at a location downstream of the fuel injector; (2) to provide for the injection of water to reduce the formation of nitrogen oxides; and, (3) to employ a construction which avoids local overheating of the components of the injector while providing recirculation of the combustion gases to improve flame stability at low fuel/air ratios.